Mechanical interlock for double doors



March 23, 1965 c. D. SMITH 3,174,193

' MECHANICAL INTERLOCK FOR DOUBLE DOORS Filed March 26, 1963 2 Sheets-Sheet 1 INVENTOR. Clara Q 544/714 BY gmz oi March 23, 1965 c. D. SMITH mzcmmcm. INTERLOCK FOR DOUBLE DOORS Filed March 26, 1963 2 Sheets-Sheet 2 INVENTOR. C ova 0 544/7 United States Patent 3,174,193 MECHANICAL INTERLOQK FOR DOUBLE B06128 Cloyd D. Smith, 14928 La Cumin-e Drive, Pacific Palisades, Calif. Filed Mar. 26, 1963, Ser. No. 267,984 Claims. (Cl. 26-46) This invention relates generally to door locks and particularly to a mechanical interlock for double doors which prevents simultaneous opening of both doors.

Some enclosures have access openings sealed by double doors which must be interlocked in such a way as to prevent simultaneous opening of both doors. So-called clean rooms, for example, are commonly provided with access openings sealed by double doors which are interlocked in this way to minimize entrance of unpurified ambient air into the rooms when the doors are opened to provide access to or from the rooms. Each such clean room has at least one large sealed access opening of this kind through which personnel may enter and leave the room and in many cases has at least one smaller sealed access, or pass-through, opening through which objects may be transferred to and from the room.

The present invention provides a mechanical interlock which is designed primarily to interlock the double doors of these smaller pass-through openings against simultaneous opening. It will become evident to those skilled in the art as the description proceeds, however, that the present interlock is adapted for use with double doors of any size and on enclosures of any type which require interlocked double doors.

Double door interlocks have been devised in the past, of course. One existing type of interlock, for example, is equipped with solenoid-operated door latches controlled by door-operated switches arranged in such manner that when either door is opened, the other door is latched shut. This type of interlock, which is used primarily on larger access doors, is quite costly, requires electrical leads to conduct electrical current to the solenoids, and is otherwise not totally practical for use with smaller double doors, such as those which are used to seal passthrough openings.

A general object of the present invention is to provide a novel mechanical double door interlock for the purpose described.

Another object of the invention is to provide a mechanical interlock of the character described which is relatively simple in construction, economical to manufacture, easy to install, reliable in operation, and otherwise ideally suited to its intended purposes.

Other objects, advantages, and features of the invention will become evident to those skilled in the art as the description proceeds.

Briefly, the objects of the invention are attained by providing a latch mechanism equipped with a latch housing adapted to be secured in fixed position between the double doors to be interlocked. Pivotally supported intermediate their ends on this housing are two identical but reversely positioned latch bars having hook formations engageable with keepers on the doors to lock the latter in closed position.

Each keeper and the latch bar for the opposing door are provided with cooperating cam surfaces which swing the latch bar to its released or unlocked position when the door mounting the keeper is closed, thereby to release the opposing door for opening. When either door is opened, the latch bar for the opposing door is returned to its latching position to lock the latter door in its closed position.

A presently preferred embodiment of the invention 7 will now be described in connection with the attached drawings, wherein:

FIG. 1 is a perspective view of the present latch installed in a pass-through opening in a wall;

FIG. 2 is an enlarged section through the latch in FIG. 1 when the doors to be latched are closed;

FIG. 3 is a section similar to FIG. 2 illustrating the latch when one door is opened;

FIG. 4 is an enlargement of the left-hand end of the latch in FIG. 3; and

FIG. 5 is an exploded perspective of the present latch.

In these drawings, the numeral 10 denotes the wall of a clean room or other enclosure having an access opening 12 sealed by double doors 14 and 16. Doors 14 and 16 are located at opposite sides of the opening 12, so as to be accessible from the interior and exterior of the enclosure, respectively, and are attached to the wall 10, as by hinges 18, for swinging between open and closed positions.

Mounted on one surface of the access opening 12, between the doors 14 and 16, is a latch mechanism 20 which cooperates with keepers 22 and 24 on the doors 14 and 16, respectively, to lock either door in its closed position when the opposing door is opened. Latch mechanism 20 and keepers 22, 24 together make up the mechanical interlock 26 of this invention.

Reference is now made to FIGS. 2 and 3 which illustrate the interlock 26 in enlarged detail. Latch mechanism 2d of the interlock comprises a housing 28 in the form of a channel having side flanges 3t) and a connecting wall 32 therebetween. Within the latch housing 28 are two latch bars 34 and 36 which extend parallel to the wall 32 of the housing. Latch bars 34 and 36 are identical but are reversely positioned, as shown. Extending through the latch bars intermediate their ends and through the latch housing wall 32 is a pin 38 which pivotally supports the bars on the housing. Spacers 40 are placed, as shown, to space the latch bars from one another and from the wall 32.

Each latch bar 34 and 36 is shaped at one end to provide a hook formation 42 including a slot 44 defining a latch shoulder 46. The adjacent end of each bar has a beveled edge surface 48. Because the latch bars are reversely positioned, the hook formation 42 of one bar is located at one end of the latch housing 28 and the hook formation of the other bar is located at the opposite end of the housing.

The opposite end of each bar has a beveled edge surface St). The beveled surfaces 48 and 50 of each bar slope in the same direction relative to the respective bar, as shown. Positioned between the flanges 36 of the latch housing 28 and the latch bars 34 and 36 are biasing means 52 which normally urge the latch bar 34 to the centered position in which it is shown in FIG. 3 and the latch bar 36 to a corresponding position. While various kinds of biasing means may be used for this purpose, the biasing means illustrated comprise sponges positioned between the latch bars and housing flanges 30.

The latch mechanism 20 is fixed in position between the doors 14 and 16 in any convenient way, such as by bolts or screws 54 (FIG. 5) extending through the latch housing 28 and the frame about the access opening. A cover 55 is secured over the latch housing 28 to conceal the latch bars 34, 36. The ends of this cover have openings 59a through which the keepers 22, 24 can engage the latch bars.

Keepers 22 and 24 are also identical and are attached to the doors 14 and 16 in any convenient way, such as by bolts or screws 56. Each keeper comprises a base 58 which seats against the respective door, a flange 60 which extends outwardly from the base, in a direction generally 0 normal to the plane of the respective door, and a transa tioned and proportioned so that when the doors 14 and 16 are in their closed positions of FIG. 2, wherein they seal the access opening 12, the beveled edge surface 50 of one latch bar 34, 36 and the hook formation 42 of the other latch bar are disposed adjacent and in line with the keeper on the adjacent door. In this closed position of the doors, the lip 62 on each keeper engages its respective confronting latch bar beveled edge surface 50, thereby camming the remote end of the bar bearing the hook formation 42 to its released position of FIG. 3 against the action of the latch arm biasing means 52. The lip on each keeper also extends toward but does not engage in the slot 44 in the other latch bar. If desired, springs or other closure means or releasable means (not shown) may be provided to releasably hold the doors 14 and 16 in these closed positions.

If one of the doors, say, door 16, is opened, the keeper 24 on the door moves out of engagement with the beveled edge 50 on the latch bar 34, thereby releasing the latter for return to its latching position of FIGS. 3 and 4 under the action of the latch arm biasing means 52. In this latching position, the hook formation 42 on the latch 34 engages over the'lip 62 of the keeper 22 on the opposing door 14, as shown in FIGS. 3 and 4, whereby the latch shoulder 46 onthe latch bar 34 is positioned behind the keeper lip to lock the door 14 in its closed position. When the door 16 is reclosed, the latch bar 34 is again cammed to its released position of FIG. 2 by the keeper 24 to release door 14 for opening.

If door 14 is opened, latch bar 36 is released by the keeper 22 on the latter door, thereby to lock door 16 in its closed position by engagement of the hook formation 42 on the latch bar 36 over the lip 62 of keeper 24. Reclosing of door 16 releases door 14 for opening.

During initial installation of the latch mechanism, both doors may be opened with the result that both latch bars will occupy their latching position. When the doors I4 and 16 are initially closed, the keeper lips 62 engage the beveled latch bar edge surfaces 48 and cam the bars to their released position thereby to permit initial closure of the doors. I

Clearly, therefore, the invention herein disclosed is fully capable of attaining the objects and advantages preliminarily set forth.

Various modifications in the design and arrangement of parts of the invention are possible, of course, within the spirit and scope of the following claims.

I claim:

1. In combination with a door frame having an access opening therethrough and a door hinged to said frame at each end of said opening, a mechanical interlock comprising:

a pair of latch bars disposed side by side within said opening in planes parallel to the central axis of said opening and extending lengthwise of the opening,

means pivotally mounting said latch bars intermediate their ends on said door frame for rocking motion in said planes, respectively,

each latch bar having a transverse shoulder at one end facing the opposite end of the respective latch bar and said latch bars being turned end for end, whereby said latch shoulder of one latch bar is located adjacent one door and said latch shoulder of the other latch bar is located adjacent the other door, a

a keeper mounted on each door including a flange projecting outwardly from the respective door and of the respective flange, and said lip of the respective keeper extends toward and is disposed for latching engagement with said latching shoulder of the other latch bar upon rocking of said one end of the latter bar toward the respective keeper flange to a latching position of the respective latch bar,

said one end of each latch bar being rockable away from its respective keeper flange to an unlatching posiition of the respective latch bar,

said opposite end of each latch bar being beveled, whereby engagement of said opposite end of each latch bar by the adjacent keeper when the respective door is closed rocks the latch shoulder on the respective bar out of latching engagement with the lip of the other keeper, thereby to release the opposite door for opening, and

means for resiliently urging each latch bar to said latching position thereof.

2. The combination according to claim 1 including:

a hollow, elongate housing completely enclosing said latch bars and having openings extending axially into its opposite ends,

means mounting said housing on said door frame, and

each keeper projecting axially through the adjacent opening in said housing into said latching position of the respective keeper when the respective door is closed.

3. A mechanical interlock for double doors comprising:

a support,

a pair of latch bars disposed side by side in parallel planes,

means pivotally mounting said latch bars intermediate their ends on said support for rocking motion in said planes, respectively,

each latch bar having a transverse latch shoulder, at one end facing the opposite end ofthe respective latch bar and said latch bars being turned end for end, whereby the latch shoulder of each latch baris located laterally opposite said opposite end of the other latch bar,

keepers at opposite ends of said latch bars each including a flange and an upstanding lip along one edge of the flange,

means for mounting each keeper on a door,

each keeper being movable between a retracted position, wherein the respective keeper is withdrawn from said latch bars, and a latching position, wherein the flange of the respective keeper is disposed in a plane substantially normal to said first-mentioned planes and engages said opposite end of one latch bar along said edge of the respective keeper flange, and said lip ofthe respective keeper extends toward and is disposed for latching engagement with said latching shoulder of the other latch bar upon rocking of said one end of the latter bar toward the respective keeper flange to a latching position of the latter bar,

said one end of each latch bar being rockable away from its respective keeper flange to an unlatching position of the respective latch bar,

said opposite end of each latch bar being beveled, whereby engagement of said opposite end of each latch bar by the adjacent keeper when the latter is in said extended position thereof rocks the latch shoulder on the respective bar out of latching engagement with the lip of the other keeper, and

means for urging each latch bar to said latching position thereof.

4. A mechanical interlock for double doors comprising:

a hollow, elongate housing having an opening extending axially into each end of the housing,

a pair of latch bars enclosed within and extending lengthwise of said housing,

said latch bars being disposed side by side in parallel longitudinal planes of said housing,

means pivotally mounting said latch bars intermediate their ends on said housing for rocking motion in said planes, respectively,

each latch bar having a transverse latch shoulder at one end facing the opposite end of the respective latch bar and said latch bars being turned end for end, whereby said latch shoulder of one latch bar is located adjacent one of said openings and said latch shoulder of the other latch bar is located adjacent the other opening,

a keeper at each end of said housing including a flange and an upstanding lip along one edge of the flange,

means for mounting each keeper on a door,

each keeper being movable between a retracted position, wherein the respective keeper is withdrawn from said housing, and a latching position, wherein the flange of the respective keeper projects into the adjacent end of said housing through the respective housing opening in a plane substantially normal to said first-mentioned planes and engages said opposite end of one latch bar along said one edge of the respective flange, and said lip of the respective keeper extends toward and is disposed for latching engagement with said latching shoulder of the other latch bar upon rocking of said one end of the latter bar toward the respective keeper flange to a latching position of the latter bar,

said one end of each latch bar being rockable away from its respective keeper flange to an unlatching position of the respective latch bar,

said opposite end of each latch bar being beveled, whereby engagement of said opposite end of each latch bar by the adjacent keeper when the latter is in said extended position thereof rocks the latch shoulder on the respective bar out of latching engagement with the lip of the other keeper, and

means for urging each latch bar to said latching position thereof.

5. A mechanical interlock according to claim 4,

wherein References Cited in the file of this patent UNITED STATES PATENTS Matchette Apr. 17, 1917 Procter Oct. 19, 1926 

1. IN COMBINATION WITH A DOOR FRAME HAVING AN ACCESS OPENING THERETHROUGH AND A DOOR HINGED TO SAID FRAME AT EACH END OF SAID OPENING, A MECHANICAL INTERLOCK COMPRISING: A PAIR OF LATCH BARS DISPOSED SIDE BY SIDE WITHIN SAID OPENING IN PLANES PARALLEL TO THE CENTRAL AXIS OF SAID OPENING AND EXTENDING LENGTHWISE OF THE OPENING, MEANS PIVOTALLY MOUNTING SAID LATCH BARS INTERMEDIATE THEIR ENDS ON SAID DOOR FRAME FOR ROCKING MOTIO IN SAID PLANES, RESPECTIVELY, EACH LATCH BAR HAVING A TRANSVERSE SHOULDER AT ONE END FACING THE OPPOSITE END OF THE RESPECTIVE LATCH BAR AND SAID LATCH BARS BEING TURNED END FOR END, WHEREBY SAID LATCH SHOULDER OF ONE LATCH BAR IS LOCATED ADJACENT ONE DOOR AND SAID LATCH SHOULDER OF THE OTHER LATCH BAR IS LOCATED ADJACENT THE OTHER DOOR, A KEEPER MOUNTED ON EACH DOOR INCLUDING A FLANGE PROJECTING OUTWARDLY FROM THE RESPECTIVE DOOR AND AN UPSTANDING LIP ALONG THE OUTER EDGE OF THE FLANGE, EACH DOOR BEING MOVABLE BETWEEN AN OPEN POSITION, WHEREIN ITS RESPECTIVE KEEPER IS WITHDRAWN FROM SAID OPENING, AND A CLOSED POSITION, WHEREIN THE FLANGE OF ITS RESPECTIVE KEEPER PROJECTS INTO THE ADJACENT END OF SAID OPENING IN A PLANE SUBSTANTIALLY NORMAL TO SAID FIRST-MENTIONED PLANES AND ENGAGES SAID OPPOSITE END OF ONE LATCH BAR ALONG SAID OUTER EDGE OF THE RESPECTIVE FLANGE, AND SAID LIP OF THE RESPECTIVE KEEPER EXTENDS TOWARD AND IS DISPOSED FOR LATCHING ENGAGEMENT WITH SAID LATCHING SHOULDER OF THE OTHER LATCH BAR UPON ROCKING OF SAID ONE END TO A LATTER BAR TOWARD THE RESPECTIVE KEEPER FLANGE TO A LATCHING POSITION OF THE RESPECTIVE LATCH BAR, SAID ONE END OF EACH LATCH BAR BEING ROCKABLE AWAY FROM ITS RESPECTIVE KEEPER FLANGE TO AN UNLATCHING POSITION OF THE RESPECTIVE LATCH BAR, SAID OPPOSITE END OF EACH LATCH BAR BEING BEVELED, WHEREBY ENGAGEMENT OF SAID OPPOSITE END OF EACH LATCH BAR BY THE ADJACENT KEEPER WHEN THE RESPECTIVE DOOR IS CLOSED ROCKS THE LATCH SHOULDER ON THE RESPECTIVE BAR OUT OF LATCHING ENGAGEMENT WITH THE LIP OF THE OTHER KEEPER, THEREBY TO RELEASE THE OPPOSITE DOOR FOR OPENING, AND MEANS FOR RESILIENTLY URGING EACH LATCH BAR TO SAID LATCHING POSITION THEREOF. 